The present invention relates to a cellular wireless network and a method of operating such a network.
A significant concern for cellular wireless networks is the handling of emergency calls made by a mobile terminal (UE). For example, Long Term Evolution (LTE) networks are packet-switched (PS) networks but emergency calls have typically been handled in the circuit-switched (CS) domain. With IMS (IP Multimedia System), it is also possible to initiate an emergency call via the PS network. However, in order for a UE to make an IMS emergency call, the UE must know if the network, typically comprising a plurality of base stations and a packet core, also termed herein a core network (CN), is IMS emergency call capable. Delays may occur if the UE cannot make an emergency call when required and must find an alternative arrangement to make the emergency call.
A solution has been proposed for use in networks complying with 3rd Generation Partnership Project (3GPP) standards in which the core network indicates the network support of IMS emergency call in the signaling procedure. However, this method by itself does not cover all scenarios, for example, it may be insufficient where the UE is in limited service state. In limited service state, for example, where a UE has no SIM, the UE may not perform any signaling procedure with the network, and thus the UE will not know if the network supports IMS emergency calls. Furthermore, the proposed solution assumes that if the core network supports IMS emergency calls, then the base station necessarily supports it also. The present inventors have realized that this assumption may not be applicable, for example, during a real deployment scenario where the core network is upgraded before the base stations are upgraded. Both the packet core and the base station to which the UE is attached must be capable of handling IMS emergency calls for the UE to be able to make such a call.
Signaling between packet core and the UE is addressed in 3GPP TS 24.301 “Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS)”.